1. Field of the Invention
The present invention relates to a fuel cell system in which hydrogen-containing fuel is supplied without using a fuel pump, and electrochemically reacted with oxygen to generate electricity, and more particularly, to a fuel cell system in which carbon dioxide produced by an electrochemical reaction between hydrogen and oxygen is used in supplying hydrogen-containing fuel.
2. Discussion of Related Art
In general, a fuel cell system generates electricity by electrochemically reacting hydrogen obtained from hydrocarbonaceous fuel such as natural gas, etc., or hydrogen-containing fuel such as methanol, etc., with oxygen in air.
The fuel cell system is a power-generating device to generate electricity by an electrochemical reaction between hydrogen (or hydrogen-containing fuel) and oxygen (or an oxidant). The fuel cell system includes an electric generator to generate electricity. The electric generator includes a unit cell (or cell unit) provided with a membrane electrode assembly that includes an electrolyte membrane having selective ion permeability, and cathode and anode electrodes provided in opposite sides of the electrolyte membrane.
The fuel cell system can be classified into a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), a polymer electrolyte membrane fuel cell (PEMFC), an alkaline fuel cell (AFC), etc., according to the kind of electrolyte used. In such fuel cell systems, the PEMFC (or PEMFC system) has good output characteristics, operates in low temperatures, quickly starts and has a short response time. Thus, the PEMFC can be used as a portable power generator. The PEMFC needs a reformer to obtain hydrogen from the hydrogen-containing fuel, which puts a limitation on miniaturizing the fuel cell system. To overcome such a limitation, a direct methanol fuel cell (DMFC) that directly uses methanol as the hydrogen-containing fuel (without a reformer) has been developed. However, the typical PEMFC and the DMFC still need to use a fuel pump, which causes noise and increases power consumption, to supply the methanol or hydrogen-containing fuel.
Korean Patent Publication No. 10-2002-0095492 discloses a DMFC (or DMFC system) in which gas produced in an electric generator is discharged to the outside through a fuel tank. Referring to FIG. 3, the conventional fuel cell system includes a fuel feeder 20 formed with fuel supplying holes 30 through which fuel is supplied to a fuel cell stack 22, and discharging gas inlets 30 through which gas is discharged from the fuel cell stack 22. However, in the conventional fuel cell system, a single opening is used as both the fuel supplying hole and the discharging gas inlet, and thus, the fuel is not smoothly supplied because of the discharged gas, thereby deteriorating the fuel cell system's efficiency in generating electricity.